HR: 11:35h
AN: T22B-06 INVITED    [Abstracts]
TI: A Mechanism to Explain the Exponential Model for Heat Production
AU: * Gosnold, W
EM: willgosnold@mail.und.edu
AF: University of North Dakota, Geology & Geological Engineering 81 Cornell Stop 8358, Grand Forks, ND 58202, United States
AB: Evidence for chemical interaction between plutons and meteoric ground water and analyses of the micro-scale and mega-scale distribution of uranium and thorium suggests that thermal convection in batholith complexes mobilizes uranium and may partially explain the exponential model for the vertical distribution of crustal heat production. Investigations of the distribution of uranium, thorium, and potassium within and around eight shallow plutons show evidence for mobilization and redistribution of uranium that was not bound in resistate-refractory minerals. Induced fission track radiography of thin sections was used to reveal the mineral associations of uranium within the rocks. Shallow plutons showing evidence of significant chemical interaction with meteoric groundwater (delta ¹⁸O) contain significant amounts of uranium in secondary hydrous minerals and secondary oxides. Plutons from deeper levels in the crust that show no evidence of interaction with meteoric ground water show uranium occurs predominately in resistate minerals such as zircon, apatite, allanite, sphene, and monazite. Thorium may behave similarly. These observations suggest the hypothesis that an exponential decrease in fracture permeability with depth likely controls the volume of hydrothermal fluid activity within the crust. Soils, sediments, volcanics, metamorphic, igneous, and sedimentary rocks contain uranium and thorium in both resistate minerals and as mobile ions. A significant amount of uranium, and possibly thorium, may be assimilated from hydrothermal fluids that interact with cooling plutons in the upper crust. Metasomatism may similarly affect the distribution of uranium and thorium in metamorphic environments.
DE: 5418 Heat flow
DE: 7218 Lithosphere (1236)
DE: 8103 Continental cratons
DE: 8125 Evolution of the Earth (0325)
DE: 8130 Heat generation and transport
SC: Tectonophysics [T]
MN: 2007 Fall Meeting